The story I am reading is The Sword Of Summer By Rick Riordan. It is the First book in the Magnus Chase and the Gods of Asgard series. The Series follows 16 year old Magnus Chase, On his Journey to delay Ragnarok. Magnus is The cousin of Annabeth Chase, Son of Frey, Owner of The Sword of Summer (also known as Jack or Sumarbrander) , and as of Chapter 7 in The Sword of Summer, he is also a dead Einherji of Valhalla. The Main antagonist seems to be Loki, but sometimes it's hard to tell what side he's on. Unlike the Loki from the Marvel franchise, Loki is never on the same side as the protagonist.
I think if they ever made a Magnus Chase movie The Immigrant song By Led Zeppelin that also appears in Thor Ragnarok, would be a great entrance song for Loki. Seeing as the Song is in a movie about Thor and Loki and Ragnarok, it seems fitting that it would be a character's theme song in another movie about trying to delay Ragnarok. Another great point is the tune makes you think of excitement and mischief, which Loki's all about seeing as he is the God of Mischief. The lyrics "We come from the land of the ice and snow" has the meaning of how Loki is part Frost Giant. The Second book in the Series is called The Hammer Of Thor and one of the lyrics of the song mention his hammer calling it "The hammer of the gods", and finally to relate it to Magnus it also says "Valhalla, I am coming!"
In The first Book Magnus goes on a Quest, with a few of his friends, to get the Sword of Summer, and make sure Fenris Wolf is still chained down. Samirah Al Abbs, A Valtrike, Daughter of Loki, who really hates her father. Blitzen, a fashionable dwarf, who has been friends with Magnus for the last two years. Lastly, Hearthstone or Hearth for Short, a deaf elf with a troubled past, who is dedicated to learning rune magic.
In The second book The Hammer of Thor, Magnus has to get Thor's Hammer back from the giants. This time though he has a little more help from Sam, Hearth, Blitzen, Jack, and a few other friends. Alex Fierro, a gender Fluid, child of Loki, who unlike Sam, embraces the powers he/she got from her/his Mom (yes Loki is his/her Mom). Mallory Keen, a Einherji, Daughter of Frigg, She died in Northern Ireland on July 21st 1972, while trying to disarm a car bomb. Thomas Jefferson Jr. or TJ for short, a Einherji, Son of Tyr, A union Soldier from The American Civil war, who died after a Confederate soldier challenged him to a one-on-one battle during the assault of Fort Wagner. Lastly, Halfborn Gunderson, a Norwegian mortal, Einherji, from Flam Norway, who died in the viking invasion of East Anglia, England.
In The final book of the series, The Ship Of The Dead, Magnus and his friends Go off on a Bright Yellow Viking ship to stop or rather delay Ragnarok and Stop Loki. This Book also has What everyone reading was hoping for it finally has Percy Jackson, The Son of Poseidon, himself in this book.